A huge earthquake has shaken Chile, killing more than 200 people, causing buildings to collapse, starting fires and unleashing a tsunami across the Pacific. With a magnitude of 8.8, it opened cracks in the earth, flipped cars and devastated the city of Concepción, 70 miles from the epicentre.

The number of dead quickly rose to 214, and is expected to increase. David Miliband, the foreign secretary, last night said there was no information yet on British casualties.

The Chilean president, Michelle Bachelet, declared a "state of catastrophe" as emergency teams scrambled over rubble looking for survivors. The Pacific Tsunami Warning Centre issued an alert for countries in Latin America as well as Japan, Russia, the Philippines, Indonesia and French Polynesia. A massive wave hit Robinson Crusoe island, the largest of the Juan Fernández archipelago, where at least three people were killed. Residents were evacuated from the coastal areas of Easter Island.

Sirens sounded across Hawaii at 6am local time (4pm GMT)on Saturday . The island's beaches were cleared as people retreated to higher ground, and tourists were moved to the upper storeys of hotels. Residents rushed to buy supplies before driving inland.

The US Geological Survey said the quake struck at a depth of 22 miles in the early hours of Saturday. It was much more powerful than the quake that devastated Haiti in January, but because it was deeper, and Chile's buildings are sturdier, there were fewer casualties.

President Bachelet said: "People should remain calm. We're doing everything we can with all the forces we have. Any information [we have] we will share immediately."

The disaster was the strongest earthquake to hit Chile in 50 years and one of the strongest ever measured. The quake shook buildings in Buenos Aires, Argentina, and was felt as far away as São Paulo in Brazil – 1,800 miles to the east.

The historic town centre of Talca, just 65 miles from the epicentre, largely collapsed. The weakest buildings, made of adobe mud and straw, were mostly commercial premises and were not inhabited at the time. Neighbours pulled at least five people from the rubble.

Collapsed roads and bridges complicated travel across the country. Electricity, water and phone lines were cut to many areas, so there was little word of casualties or damage from more remote areas. In Santiago, the capital, 200 miles north-east of the epicentre, a car dangled from a collapsed overpass; the national Fine Arts Museum was badly damaged, and an apartment building's two-storey parking lot had pancaked, smashing about 50 cars.

Bachelet said that she had no information on the number of people injured. Chile had not asked for assistance from other countries. "The system is functioning. People should remain calm. We're doing everything we can with all the forces we have," said the president.

Powerful aftershocks shook the country's coastline. There were 29 of magnitude 5 or greater, and one reaching 6.9, the US Geological Survey reported.

Modern buildings in Santiago have been built to withstand earthquakes, but many older ones were heavily damaged, including the Nuestra Señora de la Providencia church, where the bell tower had collapsed. A bridge just outside the capital also collapsed, and at least one car was turned upside down. Several hospitals were evacuated after being damaged, Bachelet said.

Santiago's airport will remain closed for at least 24 hours after the passenger terminal suffered major damage, airport director Eduardo del Canto told Chilean television. Television images showed smashed windows, partially collapsed ceilings and deserted pedestrian walkways at the airport. Santiago's subway network was closed, and hundreds of buses were trapped at a terminal by a damaged bridge.

In Concepción, Chile's second largest city, which lies 70 miles from the epicentre, nurses and residents pushed the injured through the streets on stretchers. Others walked around in a daze wrapped in blankets, some carrying infants in their arms. A 15-storey building collapsed, leaving only a few floors intact.

"I was on the eighth floor and all of a sudden I was down here," said Fernando Abarzua, marvelling that he had escaped with no major injuries. He said a relative was still trapped in the rubble six hours after the quake, "but he keeps shouting, saying he's OK", he said.

Marco Vidal, a tour director for Grand Circle Travel, who was travelling with a group of 34 Americans, was on the 19th floor of the Crowne Plaza hotel in Santiago when the quake struck. "All the things started to fall. The lamps, everything, was going on the floor," he said. "I felt terrified."

Cynthia Iocono, from Linwood, Pennsylvania, first thought the quake was a train. "But then I thought: 'Oh, there's no train here.' And then the lamps flew off the dresser and my TV flew off on to the floor and crashed."

The earthquake struck after concert-goers had left South America's leading music festival in the coastal city of Viña del Mar, but it caught party-goers leaving a club. "It was very bad. People were screaming. Some people were running, others appeared paralysed. I was one of them," said one witness.